Silver halide emulsions with increased sensitivity



United States Patent 3,320,068 SILVER HALIDE EMULSFONS WITH INCREASEDSENSITIVITY Wolfgang Miiller-Bardorlf, Cologne, and Wilhelm Saleck,Schildgen, Bergisch-Gladbach, Germany, assignors to AgfaAktiengesellschaft, Leverknsen, Germany, a corporation of Germany NoDrawing. Filed Mar. 31, 1964, Ser. No. 356,075 Claims priority,application Germany, Apr. 24, 1963, A 42,947 5 Claims. (Cl. 96-107) Theinvention relates to a method of increasing the sensitivity ofphotographic silver halide emulsions.

Numerous compounds are known which can be used as additives to theemulsion or developer to increase the sensitivity of a photographiclayer. Many different terms are used for substances that have thiseffect, e.g., chemical sensi-tizers or activators. The best known classof substances in this field are polyalkylene oxides, in particularpolyethylene oxides and water-soluble onium compounds such as quaternaryammonium-, phosphoniumand sulphonium salts or combinations thereof orderivatives of thiourea, for example, thiouronium salts.

The maximum sensitivities obtained in silver halide emulsions by theaddition of the above mentioned compounds presupposes that the silverhalide emulsions have been activated by treatment with noble metalsalts, especially gold salts.

The most commonly used combination for gold sensitization consists ofgold-(III)-salts and thiocyanate or thiosulphate, although the solutionsof thiocyanate are not very stable and those of thiosulphate arediflicult to pre pare. Reaction kinetic investigations, e.g., byProtass, Bjirrum and Kirschner (Z. Wiss. Angew. Phot. Kine l, 455(1956)) on gold complexes with thiocyanate ions admit of the assumptionthat sensitization is caused by a controlled, slow decomposition of theAu-(I)-complexes in which the thiocyanate ions participate. The mechanism of this sensitization process is not certain since many reactioncomponents are involved, such as metallic gold, Au-(I)-, Au-(IID- andthiocyanate ions, dithiocyanogen and additional sulphur degradationproducts including thiosulphate and gelatine.

Moreover, a considerable excess of thiocyanate ions is required tostabilise the gold-(I) complex and obtain maximum sensitivity of thesilver halide emulsions.

This method thus has numerous disadvantages. A considerable amount ofthe gold-(III) salts are bound by the gelatin, partly by absorption andpartly by complex formation; another amount is reduced to metallic goldand lost for chemical sensitization. In addition the large excess ofthiocyanate impairs the stability of the latent image after exposure.

It has now been found that a combined noble metal ripening and reductionripening of silver halide emulsions is obtained if the chemical ripeningis performed with salts of noble metals of group VIII of the periodicsystem of the elements having an atomic Weight greater than 100 and ofgold, particularly platinum, palladium, iridium and more preferablygold-(III) salts in the effective presence of o-hydroxybenzylaminecompounds of the following general formula In this formula, R representsa hydrogen atom or an alkyl group preferably lower alkyl up to 5 carbonatoms, which may be substituted, for example, with hydroxyl, halogensuch as C1 or Br, carboxyl, or an aryl group preferably phenyl which maybe substituted, for example with alkyl, preferably lower alkoxy, halogenpreferably C1 or Br, carboxyl, amine, hydroxyl, x represents a hydrogenatom, a hydroxyl group or a halogen atom preferably chlorine andbromine; and n is an integer between 1 and 5. The phenolic benzene ringin the above general formula can in addition be substituted, especiallyin the o-position or p-position to the hydroxy group, with lower alkylradicals preferably those having up to 3 carbon atoms which may besubstituted if desired, or with halogen atoms preferably chlorine andbromine, hydroxy or lower alkoxy groups preferably those having up to 3carbon atoms.

The following compounds exhibit particular utility: (I) (|)H@CHz-NHCH;OHOH

Galena-anteater (III) c H H3OOOHPNH-CH2-CHPOH IV on Br--CHrNHOHz-CH2OHCFOCHy-NH-OHT-CHPOH Br ort2NH cH2-om-Br l Br our on OHIOOHNHCHz-CE-C1vrn on:

CHz-OHr-OH CHrN CH2OOOH CHz-COOH uch compounds are already known. Theycan be easily reduced by reacting the appropriate substitutedsalicylldehyde with the appropriate amine. The resulting chiffs basesare hydrogenated in aqueous solution with 1e aid of a Raney nickelcatalyst. The substituent R can 1en be introduced with the aid of activechlorine comounds in an aqueous alkaline medium. In the case of rebromobenzyl compounds, the bromine can be subseuently introduced.

These o-hydroxybenzylamin-compounds are good comlexing agents for heavyand noble metal ions. For exmple, with gold-(III)-chloride,gold-(III)-cornplexes are ormed, which are often deep in color. Due tothe weakly :ducing effect of the compounds of the above general ormula,such Au-(III) complexes are reduced to Au-(I) omplexes. To ensure theformation of the Au-(l)-comlexes in every case, it is advisable toadditionally add 168k reducing agents.

The process of the invention is capable of being used Ilih allphotographic silver halide emulsions. The silver alide can consist ofsilver chloride, silver bromide, silver )dide or mixtures thereof.

An additional advantage of the process of the invention that theemulsions can be further sensitized with, for xample, sulphur compounds,polyalkylene oxides, wateroluble onium compounds or combinations ofpolyethylne oxides and onium compounds. In addition, they can eoptically sensitized by, e.g., cyanine or merocyanine lyestuffs and thelike.

Basic stabilizers can be included in the emulsions, for xample, organicmercapto compounds, quaternary benzhiazoles, triazoles,tetrazaindolizines and the like. Antther advantage of the processaccording to the invention 5 that the sensitized emulsions can be usedfor black- .nd-white photographic material or color photographicnaterial, it being possible in the latter case to incorporatelydrophobic or hydrophilic color couplers into the emulion layer.

As compared with a gold ripening using thiocyanate, ome of the compoundsaccording to the invention proluce the same sensitivity with half thequantity of gold, usually with less fogging.

The mode of addition of the o-hydroxybenzylamin- :om pounds of theinvention to the emulsions is not critical. Fhe compounds may be addedin dissolved or in solid orrn, and before, during or after the additionof the noble netal salt. Alternatively, the noble metal salt, forexlmple, gold-(IID-chloride, may be first mixed with a .olution of the ohydroxybenzylamin-compounds and then ldded to the emulsions. Generallyspeaking, this addiion is made before the chemical ripening of the emul-.ion. The chemical ripening is also called after-ripening. lhe compoundsare used in concentrations of 0.1 g. to i g. per kg. of emulsion(preferably 0.25-0.35 g./kg.). [he optimum quantity to be added dependson the reiucing power of the o-hydroxybenzylamin-compound and he natureof the emulsion. It can easily be determined Jy a few tests.

According to one preferred form of the present inven- ;ion, theo-hydroxybenzylamin-compounds are used in :ombination with weak reducingagents. Suitable for this purpose are, for example, thepolyhydroxycarboxylic acids, in particular those of the followinggeneral formula:

wherein n is 0 or an integer between 1 and 8, advantageously l5, e.g.,hydroxyacetic acid, d-gluco-ot-hexonic acid, d-gluco-a-heptonic acid,etc.

Suitable are also aldo sugars, such as glucose, dimethylformamide,nitrilotriacetic acid and similar compounds. Generally suitable for thepresent purpose are those reducing agents which are able to reducetrivalent gold to monovalent gold, but have too small a reductionpotential to precipitate metallic gold from the complexes of themonovalent gold.

The process can be varied in many ways even when using theo-hydroxybenzyl-amin-compounds in combination with the previouslydescribed weak reducing agents. The compounds can be added, in dissolvedor in solid form, before, during or after the addition of the noblemetal salt. Alternatively the noble metal salt, for example,gold-(IlD-chloride, can first of all have added thereto a solution ofthe compounds according to the invention, be thereafter reduced with'thereducing agent and then the gold-(I)-complex solution can be added tothe emulsions. The addition compounds are generally added prior to thechemical or after-ripening of the emulsion. The compounds are used inconcentrations from 0.1 g. to 5 g. preferably 0.25-0.35 g. per kg. ofemulsion with addition of 0.1 to 5 g. preferably 0.l50.3 g. of thereducing agent. The optimum quantity of the reducing agent depends onthe reducing power of the compounds and the nature of the emulsion, andcan easily be determined by a few tests. The reducing agents shouldgenerally be used in a concentration which is smaller than or at mostequal to that of the o-hydroxy-benzylarnine derivatives. The amount tobe used can be between 0.1 g./kg. of emulsion and the amount of theo-hydroxybenzylamine complexing agent.

The process according to the invention is illustrated by reference tothe following examples, without limiting the invention in any way.

Example 1 A highly sensitive gelatino-silver bromiodide emulsion with a4 mol percent of silver iodide, which contains 50 g. of silver perliter, has 35-40 mg./ liter of KBr and sulphurcompounds, etc. addedthereto for the chemical ripening in the usual way and is divided beforethe ripening into three samples A, B and C.

Sample A serves as standard sample. Before the ripening, the followingsolution is added to sample B, per lite-r of emulsion:

1 ml. of 0.08% gold-(III)-chloride solution, mixed with 3 ml. of a 10%aqueous solution of Compound I. Before the chemical ripening, there wasadded to sample C per liter, 2 ml. of a 0.08% gold-(III)-chl0ridesolution, which has been mixed with 3 ml. of a 10% aqueous solution ofCompound I.

After all three samples have been ripened until the maximum sensitivityis reached, they have a wetting agent and a stabilizer, e.g., of theazaindolizine type, added thereto and are cast onto one of theconventional film supports.

The three samples are exposed and developed in a normal commercialp-methylaminophenol hydroquinone de veloper for 10 minutes at 20 C.

The result is to be seen from Table 1.

TABLE 1 Sensitivity Fogging Gamma increase Example 2 A highly sensitivesilver bromoiodide emulsion, as described in Example 1, is pretreated asin this example and divided into three samples A, B and C.

Sample A serves as standard sample.

Sample B has added thereto, per liter of emulsion, a mixture consistingof 3 ml. of a aqueous solution of the Compound III and 1 ml. of 0.08%gold-(III)-chloride solution.

Sample C contains, per liter of emulsion, 3 ml. of a 10% aqueoussolution of the Compound III, which has been mixed with 2 ml. of a 0.08%gold-(III)-chloride solution.

The three samples are ripened as in Example 1, then coated as describedtherein onto a film support, and then the material is exposed anddeveloped as described in Example 1.

The result is shown in Table 2.

Three samples A, B and C of a silver halide emulsion as described inExample 1, are treated as follows:

Sample A serves as standard sample.

Sample B has added thereto, per liter of emulsion, a mixture of 3 ml. ofa 10% aqueous solution of Compound II and 1 ml. of a 0.08%gold-(III)-chloride solution.

Sample C contains, per liter of emulsion, 3 ml. of a 10% aqueoussolution of Compound II, which has been mixed with 2 ml. of a 0.08%gold-(III)-chloride solution.

The ripening of the three samples, the casting onto a film support, theexposure and the development is performed as indicated in Example 1.

The result is shown in Table 3.

Three samples A, B and C of a silver halide emulsion, as described inExample 1, are treated as follows:

Sample A without additives, serves as standard sample.

Sample B has added thereto, per liter of emulsion, a mixture of 3 ml. ofa 10% aqueous solution of the Compound VIII, and 1 ml. of a 0.08%gold-(HD-chloride solution.

Sample C contains, per liter of emulsion, 3 ml. of a 10% aqueoussolution of the Compound VIII, which has been mixed with 2 ml. of a0.08% gold-(IID-chloride solution.

The ripening of the three samples, the casting onto a support and theexposure and development is performed as described in Example 1.

The result is shown in Table 4.

TABLE 4 Sensitivity Fogging Gamma increase Sample A 0 0.19 0.55 +2.5"DIN 0. 26 0.55 +2.5 DIN 0. l9 0. 50

Example 5 A highly sensitive gelatino-silver bromiodide emulsion with 4mol percent of silver iodide, which contains 50 g. of silver per liter,has 35-40 mg./lit'er of KBr and sulphur compounds etc. for the chemicalripening, is divided before ripening into 3 samples A, B and C.

Sample A serves as comparison sample. Before the ripening of sample B,the latter has added thereto the following solution, per liter ofemulsion:

6 ml. of a 10% solution of the Compound I, to which are added 2 ml. of a0.08% gold-(III)-chloride solution. Thereafter, 1 ml. of a 10% solutionof sodium hydroxyacetate is added.

Before the chemical ripening of sample C, the latter has added theretothe following mixture per liter of emulsion:

4 ml. of 0.08% gold-(III)-chloride solution are added to 6 ml. of 10%solution of the compound I, the pH of the mixture is adjusted to 8 andfinally 1 ml. of 10% solution of sodium hydroxyacetate is added.

After ripening until the maximum sensitivity is reached, a wetting agentand a stabilizer, e.g., of the azaindolizine type are added to each ofthe three samples which are then cast onto a support such as paper, acellulose acetate, a polyester preferably of polyethylene terephthalateor a polycarbonate in particular of bis-hydroxyphenyl alkanes.

The three samples are exposed and developed in a commercialp-methylaminophenyl hydroquinone developer for 10 minutes at 20 C.

The result is shown in Table 5.

TABLE 5 Sensitivity Fogging Gamma increase Sample A 0 0. 20 0.55 SampleB +1.5 DIN 0.37 0.50 Sample C +3 DIN 0.15 0. 50

Example 6 Three samples A, B and C of a silver halide emulsion, asdescribed in Example 5, are treated as follows:

Sample A serves as standard sample. Before being chemically ripened,Sample B has the following solution added thereto, per liter ofemulsion:

2 ml. of a 0.08% gold-(IID-chloride solution are added to 6 ml. of a 10%solution of compound X, the pH of the mixture is adjusted to 8 andfinally 1 ml. of a 10% solution of sodium hydroxyacetate is added.

Sample C has added thereto, per liter of emulsion, a

Three samples A, B and C of a silver halide emulsion, described inExample 5, are treated as follows:

Sample A serves as standard sample. Before being hemically ripened,Sample B has the following solution dded thereto, per liter of emulsion:

2 ml. of 0.08% gold-(III)-chloride solution are added 3 6 ml. of a 10%solution of compound III, the pH of 1e mixture is adjusted to 8 and then1 ml. of a 10% olution of sodium d-gluco-a-heptonate is added.

Sample C has added thereto, per liter of emulsion, a mixture which hasbeen prepared as follows:

4 ml. of a 0.08% gold-(III)-chloride solution are added a 6 ml. of a 10%solution of compound III, the pH of he mixture is adjusted to 8 andfinally 1 ml. of a 10% olution of sodium d-gluco-a-heptonate is added.

The ripening of the three samples, the casting onto a upport, theexposure and development is performed as ndicated in Example 5.

The result is shown in Table 7.

An X-ray emulsion with 2 mol. percent of silver iodide, vhich contains80 g. of silver per liter, and which furher contains bromide and sulphurcompounds for the :hemical ripening, is divided before ripening into two;amples A and B.

Sample A is a standard sample. Before the after-ripenng of Sample B thefollowing solution is added per liter )f emulsion:

3 ml. of a 10% solution of the compound I are mixed with 1.4 ml. of a0.08% go1d-(III)-chloride solution. The pH of the solution is adjustedto 8 and 0.15 ml. of 1 10% solution of sodium hydroxyacetate is added.

After these samples have been after-ripened until the maximumsensitivity is obtained, a wetting agent and a stabilizer, e.g., of theazaindolizine type, is added thereto. Thereafter the emulsions arecoated onto a usual support. The two samples are exposed and developedfor minutes at 20 C. in an X-ray developer which yields silver imageswith a steep characteristic curve.

The result is shown in Table 8.

The procedure is as indicated in Example 8, but the following solutionis used with sample B: 3 ml. of a solution of the compound III are mixedwith 1.4 ml. of a 0.08% gold-(III)-chloride solution and the pH isadjusted to 8. There is then added 0.15 ml. of a 10% solution of sodiumhydroxyacetate. The result is shown in Table 9:

TABLE 9 Sensitivity Fogging Gamma increase SampleA 0 0.17 2.7 SampleB+l.5 DIN 0.16 2.7

Example 10 A gelatino-silver bromoiodide emulsion of medium sensitivitywith 6 mol. percent of silver iodide, which contains g. of silver perliter and which further contains potassium bromide and sulphurcompounds, etc, for the chemical ripening is divided beforeafter-ripening into two samples A and B.

Sample A is the standard sample.

Sample B, before the after-ripening, the following solution is addedthereto per liter of emulsion:

3 ml. of a 25% solution of compound I are mixed with 1 ml. of a 0.08%gold-(IlD-chloride solution. The pH of the solution is adjusted to 8 and0.5 ml. of a 25% solution of sodium hydroxyacetate is added.

After having ripened these samples until the maximum sensitivity isobtained, a wetting agent and a stabilizer, e.g., of the azaindolizinetype, are added and they are then cast onto a usual support.

The two samples are exposed and developed for 10 minutes at 20 C. in ap-methylaminophenol hydroquinone developer.

The result is shown in Table 10.

A gelatino-silver chlorobromoiodide emulsion with 20 mol percent ofsilver chloride and 6 mol percent of silver iodide which contains g. ofsilver per liter and which further contains potassium bromide andsulphur compounds etc. for the chemical ripening is divided beforeafter-ripening into :two samples A and B.

Sample A is the comparison sample.

Sample B, before the after-ripening, the following solution is addedthereto, per liter of emulsion:

7 ml. of a 10% solution of compound I are mixed with 3 ml. of a 0.08%gold-(IID-chlon'de solution. The pH of the solution is adjusted to 8 and0.3 ml. of a 10% solution of sodium hydroxyacetate is added.

After this mixture has been added to the emulsion, the samples areafter-ripened up to maximum sensitivity, thereafter a wetting agent anda stabilizer, e.g., of the azaindolizine type, are added and the samplesare cast onto a paper support.

The two samples are exposed and developed for 2 .minutes in a developerof the following composition:

Grams p-Methylaminophenol 1 Hydroquinone. 3 Anhydrous sodium sulphite 13Anhydrous sodium carbonate 26 Potassium bromide 1 Water to make 1000 ml.

It will be clear to those skilled in this art that the practice of theinvention lends itself readily to a number of useful modifications inmethod, material etc. For example, the noble metal salts are not limitedto the previously mentioned, because it is possible to use any suitablesalt which is soluble in water or lower alcohols. Such compounds are:gold halides, such as auric chloride, or complex gold halides, such aspotassium chloroaurate (KAuCh) and sodium .chloroaurate (NaAuCl However,gold compounds, such as auric sulfate, are practically as useful as thegold halides. Aurous, as well as auric compounds can be used. Complexgold salts, such as alkali metal aurous thiosulfates, alkali metalaurous sulfites (e.g., sodium or potassium aurous thiosulfate and sodiumor potassium aurous sulfite). Potassium chloroaurite, potassiumbromoaurite, potassium iodoaurite, or the corresponding sodium, calcium,strontium, cadmium or gallium salts can also be used.Pyridinotrichloro-gold, ethylenediamine-bistrichloro gold,diethyl-monobromo-gold and diethyl gold acetone and gold complexes withsulfur compounds such as are commonly present in gelatin, e.g., the goldthiosinamine complexes, can also be used.

Suitable salts of noble metals of the VIII group are ammonium orpotassium, cbloropalladate, ammonium, sodium and potassiumchloroplatinate, ammonium potassium and sodium bromoplatinate, ammoniumchlororhodate, ammonium chlororuthenate, ammonium chloroiridate,ammonium, potassium and sodium chloroplatinite, ammonium, potassium andsodium chloropalladite, etc.

The after-ripening of the emulsion with the noble metal salt and theo-hydroxybenzylamine compounds is performed at an appropriatetemperature particularly between 30 and 60 C. During after-ripening thepH of the emulsion is advantageously adjusted to the acid side ofneutrality preferably between 5 and 7. Maintenance of the emulsion onthe acid side of neutrality during coating of the emulsion is alsopreferred.

The noble metal salts are employed in an amount below that whichproduces a substantial fog. In practicizing the present invention, aquantity of the noble metal salt is employed, equivalent to between 0.1and mg. of the noble metal per :mole of silver halide in the emulsion.The noble metal compounds are preferably incorporated in the emulsion inthe form of their solutions in a suitable sol-vent such as water, methylalcohol, ethyl alcohol or the like.

We claim:

1. In a process for producing a sensitized photographic silver halideemulsion, the step which comprises afterripening the emulsion on theacid side of neutrality in the effective presence of at least onewater-soluble salt of a Group VIII metal having an atomic weight ofgreater than or gold and in the effective presence of ano-hydroxybenzylamine compound of the formula wherein R represents asubstitutent of the group consisting of hydrogen, al-kyl, and a phenyl,x stands for a member of the group consisting of hydrogen, hydroxy andhalogen and n in an integer between 1 and 5.

2. A process as defined in claim 1 wherein the phenyl ring of the benzylgrouping of the o-hydroXy-benzylamine compounds is substituted with aradical of the group consisting of hydroxy, lower alkyl, halogen andlower alkoxy.

3. A process as defined in claim 1 wherein the emulsion is after-ripenedin the further active presence of a reducing agent of the groupconsisting of polyhydroxycarboxylic acids, sugars, alphatic acid amidesor nitrilotriacetic acid.

4. A process as defined in claim 1, where the metal is gold.

5. A process as defined in claim 1, wherein the emulsion which is to beafter-ripened additionally contains at least one member of the groupconsisting of sulfur compounds, onium compounds, polyalkylene oxides anda tetraazainclolizine stabilizer.

No references cited.

NORMAN G. TORCHIN, Primary Examiner.

I. H. RAUBITSCHEK, Assistdnt Examiner.

1. IN A PROCESS FOR PRODUCING A SENSITIZED PHOTOGRAPHIC SILVER HALIDEEMULSION, THE STEP WHICH COMPRISES AFTERRIPENING THE EMULSION ON THEACID SIDE OF NEUTRALITY IN THE EFFECTIVE PRESENCE OF AT LEAST ONEWATER-SOLUBLE SALT OF A GROUP VIII METAL HAVING AN ATOMIC WEIGHT OFGREATER THAN 100 OR GOLD AND IN THE EFFECTIVE PRESENCE OF ANO-HYDROXYBENZYLAMINE COMPOUND OF THE FORMULA